This invention relates to nutritional products containing modified starches and, more particularly, to water-soluble modified starches and to nutritional products including such starches characterized by highly desirable properties.
Carbohydrates are used as the major energy source in a variety of nutritional products ranging from, for example, liquid nutritional supplements for adults with compromised digestive functions, infant formulas, and carbohydrate supplements for exercise and athletic activity. Carbohydrate supplements are likewise included in a variety of solid nutritional products.
The carbohydrates previously used as such supplements generally comprise glucose (dextrose), fructose, lactose, sucrose, and glucose polymers. Such carbohydrates typically are of relatively low molecular weight.
The use of these previously used carbohydrate sources generally exert a degree of osmolarity that, in many situations, is undesirable. Thus, the use of such carbohydrate supplements or sources can result in consequent gastrointestinal effects such as diarrhea and distention. In addition, the use of such carbohydrate sources can limit the availability of water for hydration purposes. Additionally, the high insulin responses to glucose polymers can lead acutely to elevated postprandial insulin secretion and lipogenesis, hypoglycemia, and chronically to elevated blood lipids and increased risk for cardiovascular disease.
Accordingly, to serve as the major energy source for enteral dietary formulations, other liquid nutritional supplements and other foods in general, the carbohydrate source must satisfy several criteria. From the physiological viewpoint, a suitable carbohydrate source should desirably have satisfactory glycemic, endocrine, and metabolic responses under varying physiological conditions. Additionally, no significant adverse effects on body composition and lipogenesis should result from including the carbohydrate supplement. Still further, such carbohydrate sources must be capable of being adequately digested and, preferably, have appropriate oxidation characteristics.
From the physical standpoint, the carbohydrate source should have sufficient water-solubility, particularly when used in liquid supplements so that useful amounts of the carbohydrate source can be utilized in the formulation. It is also desirable for the carbohydrate source to be capable of being readily gelatinized.
Prior literature reflects substantial work relating to the effects of starches as nutritional supplements. It has thus been suggested that the structure of food starches affects the rate of digestion of the starch as well as the glycemic and insulin responses after digestion. Behall et al., xe2x80x9cEffect of Starch Structure on Glucose and Insulin Responses in Adults,xe2x80x9d Am. J. Clin. Nutr., 47, 428 (1988); Ross et al., xe2x80x9cGlycemic Index of Processed Wheat Products,xe2x80x9d Am. J. Clin. Nutr., 46, 631 (1987).
A slow rate of starch digestion, giving low glycemic and insulin responses are likewise considered desirable for the general population, during sustained physical activity. Davis et al., xe2x80x9cCarbohydrate-Electrolyte Drinks: Effects on Endurance Cycling in the Heat,xe2x80x9d Am. J. Clin. Nutr., 48, 1023 (1988); Geske et al., xe2x80x9cPreexercise Ingestion of Glucose and Fructose: Effects on Exercise Performance When Exercise is Begun at Predetermined Time of Peak Blood Concentration of the Sugar,xe2x80x9d Med. Sci. Sports, 16 190 (1984). Such a slow rate is also desirable for use in the diets for diabetic individuals. Crapo, xe2x80x9cSimple Versus Complex Carbohydrate Use in the Diabetic Diet,xe2x80x9d Am. Rev. Nutr., 5, 95 (1985). Such a diet would lower the dependence of diabetics on deleterious high fat diets by enabling more starchy foods with lower glycemic indices to be introduced into the diet.
It has been proposed that starches with high amylose content yield more sustained plasma glucose levels with lower requirements for insulin. Behall, et al. xe2x80x9cEffect of Starch Structure on Glucose and Insulin Response in Adults,xe2x80x9d Am. J. Clin. Nutr., 47, 428 (1988). Likewise, it has been stated by Behall et al. that subsequent blood lipid and circulating insulin levels also may change after ingestion of high amylose starches.
Data has also shown that glucose and glucose polymers, fed simultaneously with calcium, can increase calcium absorption in healthy subjects and in hospitalized patients. Bei et al., xe2x80x9cGlucose Polymer Increase Jejunal Calcium, Magnesium and Zinc Absorption in Humans,xe2x80x9d Am. J. Clin. Nutr., 44, 244 (1986); Knowles et al. xe2x80x9cResponse of Fractional Calcium Absorption in Women to Various Administered and Glucose Doses,xe2x80x9d Am. J. Clin. Nutr., 48, 1471 (1988). However, it has also been noted that diets high in simple sugar can increase calcium excretion in urine by the same mechanism as dietary protein and amino acids, i.e., inhibition of reabsorption of calcium in the kidney tubules. Inhibition of calcium reabsorption by insulin is at least partially involved. Holl et al., xe2x80x9cComparative Effects of Meals High in Protein, Sucrose, or Starch on Human Mineral Metabolism and Insulin Secretion,xe2x80x9d Am. J. Clin. Nutr., 48, 1219 (1988). Accordingly, it would be undesirable to employ carbohydrates that are rapidly metabolizable, ostensibly as an aid to calcium absorption, if such carbohydrates simultaneously increased calcium excretion.
However, the use of starches characterized by a low glycemic index might serve to increase calcium absorption, particularly in the jejunum, ileum and large intestine, unaccompanied by the insulinogenic effects of glucose or the like, which block calcium reabsorption. Starches of this type might be preferred over glucose polymers in dietary products for physiological conditions where assurance of sufficient energy intake is needed and where maintenance of body calcium is most important. Conditions such as osteoporosis, diabetes, prolonged physical work, or even prolonged missions in gravity-free space are illustrative examples.
Further, the use of carbohydrates as a major energy source in a nutritional supplement pose a major problem. Typically, these carbohydrates exert a degree of osmolarity that is undesirable in many situations because of the subsequent gastrointestinal effects such as diarrhea or distention. Presently used glucose polymers, consisting of mixtures of relatively small molecular weight molecules, disaccharides and monosaccharides, do decrease the osmotic pressure somewhat in comparison to other carbohydrate sources. However, the decrease in osmotic pressure which results is generally not as much as is desired, nor is the decrease obtained very reproducible.
Still further, it would be desirable to provide starches having processing characteristic tailored to satisfy the requirements for particular applications. More specifically, sometimes it is desired to utilize starches achieving gelling at a lower temperature and requiring reduced energy. Other applications utilize retrograded starch, and it would be desirable to select retrograded starches having satisfactory gelling characteristics. In still other applications, it is desirable to enhance the pasting properties of starches, e.g., so as to reduce the paste viscosity and facilitate processing.
Additionally, one major obstacle to the use of starches for many applications is their typically characteristic water insolubility. Relatively water insoluble materials would be unsuitable for many nutritional supplements such as, for example, enteral dietary formulations and liquid nutritional supplements.
Chemical modification of starches by various techniques is also well known. For example, acid treating of starch was explored late in the 19th century. Some properties of these acid-treated starches, as compared to those of the untreated starches, include decreased intrinsic viscosity and decreased gel strength.
Also, Ma and Robyt, xe2x80x9cPreparation and Characterization of Soluble Starches Having Different Molecular Size and Composition, by Acid Hydrolysis in Different Alcohols,xe2x80x9d Carbohydrate Res., 166, 283 (1987), reported modifying potato and waxy maize starches with hydrochloric acid in methanol, ethanol, 2-propanol and 1-butanol at 65xc2x0 C. for one hour. The modified starches were readily soluble in hot water, giving crystal-clear solutions up to a concentration of at least 20% (w/v).
More recently, Fox and Robyt, xe2x80x9cModification of Starch Granules by Hydrolysis with Hydrochloric Acid in Various Alcohols, and the Formation of New Kinds of Limit Dextrins,xe2x80x9d Carbohydrate Res., 227, 163 (1992), published further results concerning treating potato starch at ambient temperature (20-21xc2x0 C.). It was observed that new types of limit dextrins can be produced by an appropriate choice of alcohol and concentration of acid.
Thus, despite prior efforts, there still exists the need for a carbohydrate source for nutritional supplements that is capable of satisfying the demanding physiological-related criteria described herein for such an application, as well as possessing the appropriate physical characteristics needed for commercial utility, while providing desired processing characteristics.
It is accordingly a principal object of the present invention to provide a starch material having the physiological responses satisfactory for use in nutritional food formulations.
A further and more specific object of this invention provides modified starches having desired glycemic, endocrine, and metabolic responses in humans under a variety of physiological conditions.
Yet another object lies in the provision of modified starches having physical characteristics satisfactory to allow use in commercial nutritional food applications.
Another object provides nutritional products containing such starches.
Yet another object is to provide a method for making such starches. A related and more specific object provides modified starches having acceptable water solubility characteristics.
A still further and more specific object is to provide a method for making such starches having altered, and desired, processing characteristics.
Other objects and advantages will become apparent as the following description proceeds.
In accordance with the present invention, it has been found that starches which are appropriately acid-treated yield modified starches that possess extremely desirable physiological characteristics when employed as an energy source for nutritional products. More particularly, such modified starches cause only a relatively slight degree of osmolarity and a low insulin response while achieving desirable blood glucose responses. A particularly preferred energy source, due to its oxidation and digestibility characteristics, can be achieved by utilizing modified corn starch, more preferably modified amylomaize-7 corn starch.
Still further, it has been discovered that starches that are appropriately acid-treated provide modified starches having altered, and desired, processing characteristics, such as gelling and/or paste profile characteristics.